1. Chapter 5 and 6- Populations
Biology I

2. What Affects Population Size?
A population is a group of organisms belonging to a single species that lives in a given area.
Populations size is affected by # of births, # of deaths, & # of individuals who enter or leave

3. Characteristics of a Population
5–1 How Populations Grow
Characteristics of a Population
1- Geographical Distribution
2- Density
3- Growth Rate
1- Geographical Distribution
-area inhabited by a population
-could be as small as a few cubic centimeters like a bacteria or as large as millions of kilometers like killer whales

4. 2- Population Density the number of individuals per unit
How organisms are dispersed can be important
Three patterns of dispersal are random, clumped, and uniform

5. 3- Growth Rate A population will grow if: Birth Rate > Death Rate
- 3 factors that affect a populations size
- number of births
- number of deaths
- number of individuals entering and leaving a population
A population will increase or decrease in size depending on the number added or removed from it
A population will grow if: Birth Rate > Death Rate
(# of individuals born) (# of individuals who die)
A population will stay the same if: Birth Rate = Death Rate
A population will decline if: Birth Rate < Death Rate

6. Population Growth Initial growth- birth (natality) is high1 2 3 4 5
Initial growth- birth (natality) is high
Exponential growth
Carrying capacity- steady state
Decline- increase in death rate
Extinction

7. Exponential Growth
If a population has abundant space and food, protection from predators and disease then the organisms in the population will multiply and the population will increase
Under ideal conditions with plenty of nutrients, heat, moisture, & light a bacteria can reproduce by splitting in half within 20 minutes producing 2 bacteria
In 20 minutes the population is 2
In 40 minutes the population is 4
In 1 hour: the population is 8
In 2 hours: 64
In 3 hours: 512
In one day: 4,720,000,000,000,000,000,000
The pattern of growth is a J-shaped curve and the population is undergoing exponential growth
Exponential growth occurs when the individuals in a population reproduce at a constant rate

8. At first, the number of individuals increases slowly, over time the population becomes larger and larger until it approaches an infinitely large size
1 million
Population size
500,000
100
One year
Under ideal conditions with unlimited resources, a population will grow exponentially

9. Logistic Growth
Exponential growth doesn’t continue in natural populations for very long
If a new species of organism is introduced into a new environment, at first the population grows slowly, then exponentially, eventually the population growth slows down (the size has not dropped, but the population is growing slower)
As resources become less available, the growth of a population slows or stops forming an S-shaped curve- logistic growth
Logistic Growth occurs when a population’s growth slows or stops following a period of exponential growth
Birth rate decreases and death rate increases

10. Carrying Capacity When growth levels off The population is not growing
Carrying capacity- the largest number of individuals that an environment can support
When a population overshoots the carrying capacity, then limiting factors may come into effect

11. Population Growth Logistic Exponential growth Limits on S-shaped curve
can be
represented by
characterized by
which cause a
Exponential
growth
Logistic
Falling
growth rate
S-shaped
curve
Limits on
No limits on
J-shaped
Constant
Unlimited
resources

12. 5–2 Limits to Growth What can limit growth? Limiting Factors
Any factor that causes population growth to decrease
Limiting factors, such as availability of food, disease, predators, or lack of space, will cause population growth to slow
Under these pressures, the population may stabilize in an S-shaped growth curve

13. Characteristics of Population Growth
J curve
S curve
Carrying capacity
Exponential growth
Time
Population
DISEASE
SPACE
PREDA-TORS
FOOD

14. Density-Dependent Limiting Factors
A limiting factor that depends on population size is a Density-dependent limiting factor
Density-dependent factors include disease, competition, predators, and parasites.
Disease, for example, can spread more quickly in a population with members that live close together.
Density dependent factors create an S-shaped curve
Organism Interactions Limit Population Size
Population sizes are limited not only by abiotic factors, but also are controlled by various interactions among organisms that share a community.

17. Predation affects population size
Predation is a density-dependent factor
When a predator consumes prey on a large enough scale, it can have a drastic effect on the size of the prey population
Populations of predators and their prey are known to experience cycles or changes in their numbers over periods of time

18. Competition within a population
Competition is a density-dependent factor
When only a few individuals compete for resources, no problem arises
When a population increases to the point at which demand for resources exceeds the supply, the population size decreases
Competition can also occur between members of different species- this creates evolutionary change
The two species competing are under stress to change in way that decrease competition- eventually evolving to occupy separate niches

19. ___ _____
Moose
Wolves
The periodic increase in the moose population is quickly followed by a rise in the number of wolves.
This increase in the number of wolves increases the number of moose captured by their predator and the moose population drops.
The wolf population will then decrease after the moose numbers drop because the wolves are less able to find food.
The predator prey cycle can be repeated indefinitely.

20. Parasitism and Disease
Parasites can also limit a population’s size
Parasites are similar to a predator in that they take nourishment at the expense of their host

21. Density-independent limiting factors and population growth
Density-independent factors can affect all populations, regardless of their size
Most density-independent factors are abiotic factors, such as temperature, storms, floods, drought, and major habitat disruption

22. Density-Independent Factors
Density-independent factors create a population crash
(exponential growth followed by a sudden collapse)
Examples:
Weather- a drought kills grass
Human activity: deforestation- destroys habitat
Seasons: a severe winter regulates insect population

23. Population Growth after a Density- _____________ Limiting Factor
Time
Population
Density

24. Limitations on Population Growth

25. Reproduction Patterns
In nature, animal and plant populations change in size.
Biologists that study the factor that determines population growth— Demographers

26. Demography 5–3 Human Population Growth
Demography, the study of human population size, density and distribution, movement, and its birth and death rates
Demography examines the characteristics of human populations and attempts to explain how those populations will change over time
Demographic transition- a change in a population from high birth and death rates to low birth and death rates; Examples- United States and Japan

27. Human Population Growth
Industrial Revolution Begins
Industrial
Revolution
begins
Agriculture
begins
Agriculture
begins
Bubonic plague
Plowing and irrigation
Bubonic
plague
Plowing
and
irrigation
Until about 500 years ago, the population grew slowly.
Agriculture, industry, & sanitation made life easier and safer.

28. Human Population We are growing exponentially
Due to technological advances: medicines, a dependable food supply, and sanitation
The death rate is decreasing and the life expectancy is increasing
The human population will eventually reach its carrying capacity

29. Age Structure
Population Distribution Per Age Range for Several Countries
Stable growth
Rapid growth
Slow growth
Male
Reproductive years
Female
Age
Population (percent of total for each country)
Population growth depends on how many people of different ages make up a given population
Demographers can predict future growth using age-structure diagrams
Age-structure diagrams graph the number of people in each age group

30. Age Structure
U.S. Population
Rwandan Population

31. Ch.6-2: Human Impact on the Environment
Air
Greenhouse effect
Trapping of heat by gases in the Earth’s atmosphere (carbon dioxide)
This may lead to global warming- increase in the Earth’s temperature from the rapid buildup of carbon dioxide and other greenhouse gases
Acid Rain
Burning of fossil fuels release nitrogen and sulfur into the atmosphere which combined with water form nitric and sulfuric acid
Acid Rain kills plants
Smog
Mix of chemicals in the air from automobile exhaust
Affects the respiratory system especially those with asthma

32. Human Impact of the Environment
Water
Excessive nutrients can cause an increase in algae growth and depletion of oxygen for other organisms
Over harvesting of fish has reduced the number of fish

33. Human Impact of the Environment
Land
Erosion
The wearing away of surface soil by water and wind
Desertification
The combination of farming, overgrazing, and drought in dry climates which turn productive areas into deserts
Deforestation
The loss of forests which leading to severe erosion and changes in soil properties

34. Humans need to learn to be a part of nature not apart from nature!
Consequences
If humans continue to alter the environment, they will have to deal with the results
Examples: deforestation, ozone layer destruction, global warming
Humans need to learn to be a part of nature not apart from nature!

35. Ch. 6-3: Biological Diversity
Ecosystem diversity- variety of habitats, communities, and ecological processes in the living world
Species diversity- the number of different species
Genetic diversity- sum total of all the different forms of genetic information carried by all organisms living on Earth today
Biodiversity increases as you move toward the equator.
Areas around the world differ in biodiversity
Biodiversity can bring stability to an ecosystem.
Biodiversity is one of the world’s greatest resources

36. Variations within a species also helps protect against disease or parasite
Genetically different individuals within a species have a better chance of resisting disease
Example: world cheetah population reduced by a single virus
Tree plantation has same type of trees (single species) vulnerable to disease, etc..- spread easily
Diversity among individuals in a population is important to resistance of population as a whole (genetically different)

37. Species Diversity Insects Protists Other Animals Plants Bacteria Fungi
54.4%
Protists
Other Animals
4.2%
19.7%
Plants
18%
Bacteria
Fungi
0.3%
3.4%

38. Loss of Biodiversity
Extinction is the disappearance of a species when the last of its members dies
Extinction is a natural process and Earth has experienced several mass extinctions during its history
A species is considered to be an endangered species when its numbers become so low that extinction is possible

39. Threats to Biodiversity
Complex interactions among species make each ecosystem unique
Changes to habitats can therefore threaten organisms with extinction
Human activity can reduce biodiversity by altering habitats, hunting species to extinction, introducing toxic substances into food webs, and introducing invasive species
Habitat loss-One of the biggest reasons for decline in biodiversity

40. Threats to Biodiversity: Habitat fragmentation
Habitat fragmentation is the separation of wilderness areas from other wilderness areas
Habitat fragmentation creates “islands” of habitat that are isolated from each other

41. Threats to Biodiversity: Demand for wildlife products
Hunting has caused many animals to go extinct
Humans hunt for food, fur, hides, and body parts
In the United States animals are protected from hunting if they are endangered

42. Threats to Biodiversity: Biological Magnification
Fish-Eating Birds
Magnification of
DDT Concentration
Threats to Biodiversity: Biological Magnification
10,000,000
Increasing concentrations of a harmful substance in organisms at higher trophic levels in a food chain or web
Example: DDT
Large
Fish
1,000,000
Small Fish
100,000
Zooplankton
10,000
1000
Producers 1
Water

43. Threats to Biodiversity: Invasive Species
Invasive species threaten biodiversity
Invasive species are organisms that have been introduced into new habitats and often become invasive, reproduce rapidly
Invasive species lack density-dependent limiting factors to keep their populations in check and take over areas and out compete existing species
Native to South America, nutrias have become pests in coastal areas of se US. These furry rodents eat water plants that protect fragile shorelines from erosion. This destroys the habitats of species native to those ecosystems.